In the production of polymers of acrylonitrile useful in the formation of fibers by melt-spinning, the prior art procedures have comprised formation of the polymer by polymerization of the monomer, such as taught by Mallison in U.S. Pat. No. 2,847,405. A polymer crumb is formed, stripped, washed and dried to a low moisture level for ultimate fiber formation.
The drying of the polymer crumb is normally conducted after the polymer recovered from the polymer washing zone has undergone a series of treatments such as additive blending, compounding, pelletizing etc. The crumb, in the form of pellets, is normally dried on a belt drier and then conveyed to a suitable storage area or directly to the melt-spinning facility. The steam generated during the crumb drying is vented and lost.
Before spinning, the moisture in the polymer is normally adjusted by blending therewith the required amount of water, to obtain about 15 weight percent. The resultant mixture of polymer and water remains as a powder and must be formed into a melt before spinning can be accomplished.
U.S. Pat. No. 3,991,153 discloses a method for forming the polymer melt which is ultimately formed into fibers whereby the wetted polymer containing up to about 35-40 weight percent of water is compressed and melted in an extrusion zone with the aid of a porous plug which prevents the escape of vaporized water. U.S. Pat. No. 4,283,365 is an improvement on the above-patented extrusion process and comprises the use of a vertically disposed compression zone. While generally effective, both of these systems still require the handling of a delicate pellet, the close control of moisture and the proper extrusion procedure.
U.S. Pat. No. 3,847,885 avoids some of the problems attributed to the above systems in that it discloses the creation of a polymer melt in an excess of water, however, the procedure requires that the system again be cooled. A reverse solidification of the polymer results with the hope that the required, critical amount of water will remain entrapped therein.
Each of the above procedures involves difficulties and undesirable features which, if eliminated, would solve a long-felt need and result in considerable savings in both energy and handling.